The present invention relates to a light sensitive material for making a lithographic printing plate therefrom using silver complex diffusion transfer process (DTR process) and especially to a light sensitive material for lithographic printing plate having as a support a polyester film coated with an organic copolymer composition for rendering it hydrophilic and increasing adhesion thereof.
A method for making a lithographic printing plate using DTR process, more particularly, a method comprising imagewise exposing a light sensitive material comprising a support, at least one light sensitive layer provided thereon and a physical development nuclei layer to which the image recorded on the light sensitive layer is reverse-transferred and which is provided on said light sensitive layer and then subjecting the exposed material to silver diffusion transfer development to form a metallic silver image on the outer surface of the material is called "direct plate making method". This method is more advantageous in simplicity and rapidity than conventional methods which use a lith film as an intermediate process while it has the problem in printability that only less prints can be obtained and various improvements have been made therefor.
The same can be applied to the lithographic printing plates basically disclosed in U.S. Pat. No. No. 3,728,114 and this has been considerably improved in printability by the lithographic printing plate disclosed in U.S. Pat. No. 4,230,792.
In the above mentioned patents various supports have been disclosed. With increase in printability, plastic films have been used as a support considering elongation of plate or penetration of water thereinto during printing and a polyester film has been mainly used because of its superior mechanical properties, dimension stability, heat resistance, chemical resistance and transparency.
However, as well known, polyester films are generally high in crystallinity and chemically inert and high in chemical resistance. Besides, since it is not hydrophilic and is highly hydrophobic, further various improvements have been attempted in order to obtain good adhesion to the hydrophilic photographic layers.
For example, there have been proposed such methods as subjecting a polyester film to surface treatments such as chemical treatment, mechanical treatment, discharge treatment, flame treatment, ultraviolet ray treatment, high-frequency treatment, plasma treatment, laser treatment, mixed acid treatment and osonic acid treatment and then directly coating photographic layers thereon. (cf. U.S. Pat. Nos. 2,943,937 and 3,475,193 and British Pat. No. 1,215,234). However, these surface treated polyester films are enhanced in adhesion to hydrophilic layers, but sufficient adhesion strength cannot be obtained.
Further method has been proposed according to which an organic copolymer composition layer is provided on films after surface treatment in order to increase adhesion to hydrophilic photographic layer, namely, so-called subbing layer coating method.
This method can be classified to the following two methods:
(1) A method comprising coating a composition composed of an organic copolymer and an organic solvent which is a swelling agent or dissolving agent for polyester films (referred to as "solvent subbing method" hereinafter). (cf. U.S. Pat. Nos. 2,830,030 and 4,093,458 and British Patent Nos. 772,600, 776,157 and 785,789).
(2) A method comprising coating an aqueous composition (so-called latex) of an organic copolymer containing substantially no organic solvent (referred to as "aqueous composition subbing method"), namely, swelling agent or dissolving agent for hydrophobic support such as polyester is not used and there are used copolymers of, for example, vinyl chloride, vinylidene chloride, methacrylic acid, acrylic acid, itaconic acid, maleic anhydride, styrene and butadiene which are disclosed in U.S. Pat. Nos. 4,128,426, 4,241,169, 4,265,946 and 4,394,442.
The solvent subbing method (1) is being switched to the aqueous composition subbing method (2) due to deterioration of polyester film caused during subbing process or the problem in safety and environmental pollution caused by gas of the organic solvent.
However, it has been found that both of the methods have severe defects in that when as a result of improvement in printability, number of prints must be increased or when a special ink such as ultraviolet ray curing ink is used, the photographic layer peels off from support (so-called "peeling of layer") before the problem of wearing-off of metallic silver or problem in water retention become significant, although there are no problems when the subbed film is used for general photography or when used as a support for lithographic printing plate disclosed in U.S. Pat. No. 3,728,114 or when many prints are not printed.
This phenomenon of peeling of layer is considered to be caused by organic solvent in printing ink and there have been not yet found subbing methods which bring about no peeling of layer, although the phenomenon depends somewhat on the kind of organic copolymer used for subbing layer or subbing method. This is an important problem for lithographic printing plates (especially for those which are used for printing of a large number of prints) which use a polyester film as a support and utilize DTR process.